The present invention is directed to a tubular package of glass fiber strand or strands having improved pay-out, when the glass fibers are removed from the package. More particularly, the present invention is directed to a package of continuous glass fiber strand or strands, where the strand or strands can be removed from the package from the inside of the package to the outside of the package so that most or all of the strand or strands in the package can be removed from the package.
Continuous glass fiber strands are formed from numerous, fine, individual glass fibers, which are attenuated from small orifices in a bushing, which contains the molten glass. During forming the glass fibers are treated with a binder or sizing composition and then gathered into strands and wound around a mandrel into a package. The winder usually provides the attenuation forces necessary to from the glass fibers from the orifices of the bushing. The resulting wound package is usually dried and the dried package is ready for further processing or for shipment.
In further processing of the dried package of continuous glass fiber strand or strands, many of the strands may be combined and wound in parallel without a twist into what is known as a roving package. Rovings are made by placing a number of packages from forming on a creel and collecting the strands from each package together and passing them through guide eyes and tensioning devices, and then winding the strands together as one bundle of strands onto a winding machine that is standard in the industry. In addition to producing the roving packages from packages of glass fiber strand from forming, the art has developed the method and necessary apparatus for forming precision wound roving packages of glass fiber strands directly during the glass fiber forming process. The roving packages from either production process generally have an exterior cylindrical shape with a flat surface at both ends of the package. The package also has an internal longitudinal cylindrical cavity present because of the mandrel on which the package was wound. Continuous strands can be removed from these cylindrical roving packages and used as reinforcement of polymeric or elastomeric materials, or for chopping or weaving or impregnation with a resin for applications such as filament winding and pultrusion.
Generally, the users of roving packages prefer to remove the roving or bundle of strand or strands, hereinafter referred to in the specification and claims as "strands", from the package from the internal cavity to the exterior cylindrical surface. Also, users like to have two free ends of strands in the internal cavity so that one end can be tied to the free end of another package and as the strands are removed from the first package, the tied ends automatically transfer the feed to the second package, when the first package is totally drawn. Therefore, users of roving packages and other packages of continuous glass fiber strands desire that the strands within a package can be totally drawn from the package. This drawing of the strands from the package is referred to in the art as the pay-out of the strands.
Several problems arise from the unwinding of the strands from the inside of the outside of the package. As the package is unwound, the shell of the package, i.e., the remaining strands present in annular overlapping layers, becomes thinner. This may eventually lead to the package becoming unstable so that the shell may collapse in upon itself. Such a collapse would cause the remaining strands to become entangled. This results in the balance of strands from the package being discarded and decreases the efficiency of continuously drawing strands from one package to the next. Another problem that may arise if the package shell does not collapse in upon itself, is that the remaining package may become so light that pulling the strand from the inside lifts the package entirely rather than unraveling the last few layers of strands from the package. This lifting of the package would be due to the inability of the weight of the light package to overcome the adhesive forces between the strands, which are generated from the binder or sizing composition present on the strands. This again leads to tangles and requires the discarding of the balance of the package, and again, decreases the efficiency of continuously drawing the strands from one package to the next.
The art of removing glass fiber strands from the interior of a package to the exterior of the package has suggested several solutions to the problem of not obtaining complete pay-out of the strands from a package of strands. An early attempt is described in U.S. Pat. No. 2,630,280, where the roving package was placed in a chamber. On the top of the roving package was a washer-like member that acted as a strand guide and as a restraint to any vertical movement of the package. Collapse of the package was prevented by creating a vacuum in the chamber in which the roving package was located to thus force the walls of the roving package against the walls of the chamber. But such an apparatus involves the use of a cumbersome support apparatus such as a vacuum pump.
More recently, the art has approached the problem by providing several different package coverings. For instance, shrink wrap polymeric films have been used alone or in combination with kraft paper or an adhesive support layer. Also, a collapsible elastic membrane has been suggested for wrapping the roving packages, where the membrane is used alone or with a control layer interspersed between the layers of the elastic membrane. With the use of the control layer, the collapsible elastic membrane collapses less than when the collapsible elastic membrane is used alone. The use of heat shrink polymeric films is expensive because of the cost of the heat shrink film and of the equipment needed to shrink the film around a package of strands. Also the energy needed to shrink the film adds to the cost of using such materials. With the use of collapsible elastic membranes, the stretched protective wrap around the package of continuous glass fiber strand may collapse in on the strands or dislodge the strands when only a few layers of the glass fiber strand are left to be drawn from the package. Such a collapse or dislodging may cause the protective film to be entangled with the strands being drawn so as to cause the film to be drawn along with the continuous glass fiber strand. This decreases the efficiency of continuously drawing glass fiber strands from one package to another.
Therefore, the art is still searching for a package of continuous glass fiber strands, where the package can be completely paid-out, i.e., all of the strands that are in the package can be removed. Such a package would improve the efficiency of drawing glass fiber strands from one package and connecting the glass fiber strands of one package to the glass fiber strands of another package for removal of the strands from the second package.
It is an object of the present invention to provide a package of glass fiber strands wound in superimposed annular layers that is unwound from the inside to the outside of the package and that has improved pay-out of the glass fiber strands wherein slumping of the various layers of glass fiber strands is reduced and the pay-out of the strands from the package is improved, and the transfer from strands of one package to the strands of another package is improved.
It is a further object of the present invention to provide a method of producing a package of glass fiber strands wound in superimposed annular layers that can be unwound from the inside layer to the outside layer of the package, wherein slumping of the various layers of glass fiber strands is reduced and the pay-out of the strands from the package is improved, and the transfer from strands of one package to those of another package is improved.